Transmission control



Nov. 3, 1931.

R. c. MATHEs TRAN'SMISS'ION CONTROL 3 'Sheets-Sheet l Filed June ll.1929 5 Sheets-Sheet 3 Sudam, S w H R. C. MATHES "TRANSMISS ION CONTROLFiled June 1l Nov. 3, 1931.

Patented ov. 3, 1931 e UNITED ySTATES .PATENT OFFICE ROBET O. MATHES, l'WYOMING, NEW

JERSEY, .ASSIGNOR TO BELL TELEPHONE' LABORATORIES, INCOPORAT'ED, OF NEWYOBI, N. Y.; A COBPORATIIIONKOF NIW YORK 'Application mea :une n,

This v invention relates to electric wave transmission systems,particularly to twowa'y electric communication systems.

The invention inits broad aspect-relates I6' to the controlling oftransmission in a signal transmission system by control lenergytransmitted over the system under control of signals, and in advance ofthe signals, to opery ate circuit-control means at one or vmore 10points in the system.

An object of the invention is improve the operationofa signaltransmlssion system including circuit-control means operating undercontrol 'of the signals transmlttedlover the system. l

The invention is especially applicable. to a system over which two-waytransmlsslon of signaling energy is required withln the same frequencyrange, and mcludmg as a link therein a long section of two-way cable ofhigh attenuation, such as a dee sea submarine cable. Signal-controlledcircuit-control ap aratus,"for example, so-called slngm and ec oSuppressors, are usually assoclate with the oppositely directedampllfymg paths at each terminal4 of the cable 1n such a system toinsure that the stem 1s operative to.- transmit in only one dlrection ata tune, so as to effectively suppress echoes, singing or both. This isusually accomplished by mak ing the circuit-control apparatus at eachter- -m1nal responsive to 4transmission 1n one direction to'make thecircuits thereat operative foi-transmission in that direction and toef-.

fectively disable the .circuits `for transmission in the oppositedirection.

There are two main characterlstics of such a system, the combination ofwhich mayY introducev diiiculties in the application of such.signal-controlled, circuit-control apparatus thereto. One of these isthe increased time of transmission over the cable due to its length andloading, and the other is the high att'enuation of the cable.Theincreased time 02E-transmission over the cable atly increases thechance that two subscri ers at .the ends of the system may .both starttalking within the time interval.

equal to the transmission time of the cable, lresulting ,1n eachsubscriber 'by'means of his frmnsuissroN cominci.

1929.v serial No. 370,035.

,of a'v sustained alternating current wave,

called the courier, under the control of the speech waves, Afrom eitherterminal over the cable or an\ auxiliary circuit ahead of the speechwaves to condltion the circuits for repeating in the direction of speechwave transmission. A method of vthis general nature is adapted for usein a cable system such as described above, but must be considerablymodi- 4fied because of characteristics peculiar to the ystem, such asthe very high attenuation and e limited, useful frequency range andloadcapacity of the cable to make it practicable for commercial use from-thestandpoint of quality and economy.

To operate csuch a s stem it is necessary to. have information at othends of the cable 80 as to when talk is going in at either end, and thisinformation may have to be'positively received through talk going outfrom the other end. The direction of energy ow is of little value ingiving such information as the weak speech energy incoming from thecable at one terminal may bel completely lost among the reiectedcomponents of the outgoing speech. This information is preferablycarried in accordance with the invention by auxiliary vwaves otherthanthe speech waves. The difficulty associated with applying such auxiliarywaves to the cable simultaneously with the speech waves whose presencethey are to indicate is that they will use up part of the load carryingcapacity of the transmitting amplifier and, more important still, of theloady capacity of the cable, if interference through intermodulation isto be avoided.

The above mentioned dificulties in a system ma* of the ltype describedhave been substantially minimized` in accordance with the invention by amodification of the courier method of control. In the method of theinvention, the signal energy generated at each terminal of the cable orincoming from a land line connected thereto 'is made to control thesending out over the transmission circuit ahead of thesignals, of ashort train of alternating current control Waves, which will be referredto hereafter as the courier, of frequency different vfor each terminaland outside `the speech frequency range to operate circuit-y controlmeans to establish initial control in proper time relation of thetransmitting and receiving circuits at each terminal of the sys- .temand of any intermediate repeater circuits, this control being maintainedby the speech energy when it arrives at the controlling points. The rstcourier sent out will determine whichterminaI or talker gets exclusivecontrol of the system.

' One type ofterminal circuit utilizing the general method of control ofthe invention may be used in connection with a system h avingcharacteristics such that it is feasible therein to select the incomingcourier in the presence of simultaneous .outgoing speech energy, suchyas a system employing a short cable or one of lesser overallattenuation. Another type of circuit utilizing this general method of`control may be used with a system having characteristics such that itis not feasible therein to select the courier in the presence ofsimultaneous outgoing Aspeech energy, such as a system employing a verylong cable or one of very high overall attenuation.

My copending application Serial No.

)370,034,4iled J une 11, 1929, is specifically directed to circuits ofthe former type.

This ap lication is specifically directed to circuits ofp the lattertype, these circuits being arranged softhat the courier is sent out farenough Aahead of the speech so that initial control is established-forone terminal or the other before speech energy is actually applied tothe cable, thus preventing any interference with the courier by out oingi stood from the followi speech energy or loss of any part o the speech.A

rlhe exact nature and the obects and advantages of the invention will better underdetailed description thereof, when read 1n connection with theaccompanyingdrawings, in which Fig.-

l--A shows ay schematic dia am illustratingthe principle -oftheinvention a igs. 1 and-2 show circuit diagrams of diferent types ofcable terminal circuits embodying the 1nvention;"and

Fig. 3 snows a clrcuit diagram of an in termediate repeater' stationembodying' the invention, which repeater station may beA used to coupletwo sections of cable, having mission time of the cable.

rasato@ lterminal stations such as Asltown .in Fig. 2 or 3.

For convenience the invention will be described as applied to systemsfor the twoway transmission of speech waves, but it is apparentthat theprinciples thereof apply equally Well to systems for the transmission ofsignal Waves in general comprising-frequencies within or outside thespeech frequency range, such asy waves representing' speech,entertainment programs comprising music as `well as speech, etc.

Theschematic diagram of Fig. l--A illustrating the principle of theyinvention will be first described. In the system shown in that ligurethe speech wave l controlsthe sending out'of a short train of controlWaves 2, which will be' referred to hereafter as the courier ahead ofthe speech Wave, over the cable 3 from one terminal -thereof tol theother. As

indicated in the figure, the courier 2 precedes the speech Wave 1intransmission over the cable 3 by 'a time interval T.' In the mannerdescribed in detail in connection with the circuits of the otherfigures, the transmitted courier 2 may be'utilized to establish initialcontrol of switching circuits at both terminals of the cable and atintermediate repeater points to, condition the apparatus thereat forefficient transmission in the direction of the speech waves only, whichcontrol will be maintained by the speech wave 1 on its arrival at thecontrol points. Thetime interval T is substantially equal to the fulltransmission time of the cable 3, so that the initial control of theswitching circuits at the far terminal is established for one terminalor the other before any speech energy actually is applied to the cable.

Figs. 1 and 2 show alternative types of terminal circuits for a two-waycable system employing the general principle outlined in connection withFig. 1-A to prevent transmission lockouts when two subscribers at oposite ends of the system both start talking within the time interval eual to the transince the terminal stations at both ends ofthe cablesystem may be substantially identical in construction, except for thevalues of the frequencies of the courier currents transmitted from eachstationand the range of some of the filters employed, itfhas been deemedsufficient to ilvlustrate the terminal station at one end ofthesystem'only. the east stat-ion,-and in the following description themanner of the operation of the system will be clear from reference tothe single vstation shown.

The terminal station of Fig. 1 comprises ',a transmitting circuit TA anda receiving circuit RA are ,connected to the east end of the fier 5,.The receiving circuit RA comprlses reading ,from west lto east, the bandpass filter 6, the band pass filter 7 ,and the one-way receivingamplifier 8. Connected to the transmitting circuit TA between thecircuit TL v and the input of delay circuit 4 is a control circuit 9comprising the current-controlled relay-controlling device 10, and thefast-operating relay 11 and the slow-operating relay 12 connected inparallel to the output of the device 10. The normally open switch 13connected to a generator 14 of alternating currents of frequency f2which may be any frequency outside the speech frequency range, isadapted to be closed by operation of the krelay 11 to connect thegenerator 14 across the transmitting circuit TA in the output of thetransmitting amplifier 5 therein. The

normally closed switch 15 also connected to generator 14 is adapted tobe opened by oprelay eration of the .relay 12 to disconnect thegenerator 14 from the transmitting circuit TA.

Connected to the transmitting circuit TA' between the output of thedelay circuit 4 and the input of amplifier 5 is a second control circuit16 comprising the current-controlled relay controlling-device 17 andthe18 connected to the output of the devlce 17. .y l

Connected tothe receiving circuit RA between the band pass filters 6 and7 therein' is"a third control circuit 19 comprising thecurrent-controlled, relay controlling device 20- and the relays 2l to 23connected in par allel to the output of the device 20.

A normally closed switch 24 in the inputcircuitigof control device 20 incontrol circuit 19 is adapted to be opened by the operation of relay 18.A normally closed switch 25 in the transmitting circuit TA between thepoint of connection of control circuit 16 .thereto and theoutput ofdelay circuit `4, and a normally closed 4 switch 26 in transmittingcircuitTA betweenthe connection of control circuit 9 thereto and thecircuit TL arel adapted to be opened by operation of relays "21 andj 22,respectively. A normally open v ,-,sw1tch27 in receiving circuit RAbetween the output of 8 therein and the circuit TL is adapted to beclosed by the oper-I ation of relay 23.

It is seen that the terminal circuit which has just been described is ofthe form which is known in the art' as semi-biased, that is, the circuitis normally operative vfor'transmission in one direction (in this casefrom east to west) andv transmission in the opposite direction dependsupon a switching operation.

The control devices 10, 17 and 20 may be vacuum tube'amplifier-rectifier devices of the type well known in the art or anyother devices vvhicli will respond to alternating current impressed ontheir inputs to control the operation of a relay or relays in the outputthereof.

l The one-way delay circuit 4 may be of any type forproducing a delay ofthe required amount, which will be specified below, in alternatingcurrents translnitted therethrough, as for example, a low pass filter,such as disclosed in the U. S. Patents -to Campbell 1,227,113 and1,227,114, issued Mayv being described. .The frequency f1 may be Aanyfrequency outside the speech frequency range and differing from thefrequency f2.-

The filter at the west terminal station correspondlng to the filter 6 atthe east terminal station 1s designed to pass frequencies Within thespeech frequency range and the courier frequency f2.

The one-way amplifiers 5 and 8, the mechamcal relays r11, 12, 18 and 21to 23 and the generators utilized at the east and west terminalstations, respectively, for generating courier frequencies f2 and f1'may be of any of the types Well known in the art.`

As the system operates in similar manner when telephonie transmission isset up first in the direction from east tovwest as when telephonictransmission is set up first in the opposite direction, the operationofthe system for the former case need onl be described. It will be assumedthat te ephonic currents for transmission from east to west are firstset up at the east terminal .station (the station shown in Fig. l), andthat not more than T seconds later` where T is the total transmissiontime of the cable TC between the east and west terminal stations,

.telephonie currents are set up at the west The `westwardly directedtelephonie currents'from the sourceTL are impressed directly'upon thetransmitting circuit TA. A

' small portion of the impressed currents are diverted' into controlcircuit 9 and operate the control device -therein which causes th'ewindings of'relays 11 andy 12 to be energized. The relay 11 will quicklyoperate to close the switch 13 so as to connect the source 140i courierfrequency f2 across the transmittingl circuit'. TA.. Slow-operatingrelay 12r will operate `an instant later to open the switch 15 so asftodisconnect'the generator 14 trom-thetransmitting circuit TA.' Thiswillcause a short .impulse'of current of frequency. f2, which we will refertohereafter as the courier fg, tobe transmitted over the transmittingcircuit TA. The transmitted impulse may be made .as shortyas is desiredor as is necessary by the design of relays 11 and 12..

The relays 11 and 12 are so designed that they will remain operated aslong as speech waves from the source TL are being su plied to thecontrol device 10. They are designed so that they will release onlyaftera complete pause in a conversation and not for the usual pausebetween words or syllables.

The courier f2 will be impressed upon thev l l cable. TC by the hybridcoil I-I1 andtransmittedl over the. cable to the west terminal station,where it will establish initial control of the switching circuitsthereat in a manner which will be described later.

The main portion of the telephonic cur- .rents impressed by the line TLupon the transmittingI circuit TA will be .passed through the one-waydelay circuit 4 .being delayed therein for a time interval of T seconds,where. T is the totalftransmission time of the cable T C betweenthe eastand west terminal stations. The telephone currents passed by the delaycircuit 4f' will be divided between thecontrol circuit 16 and the input.

of the transmitting am 4liiier 5. `The main portion of the passed teephone currents will be amplified by the transmitting amplier 5 andimpressed by the hybrid coil 1 on th'e cable TC following the courier f2in transmission thereover by the time interval T.

i' A small ortionof the telephonie currents passed by t e delay circuit't willbe diverted into control path 16 and will operate the controldevice- 17 therein, which in turn will energize. the relay 18. Thecontrol device 17 should not operate. unless control device 1G.

has been' previously operated by the Vtelephonie currents. The vrelative sensitivities of control devices 10 and 17 ,so that the latterwill be operated in response to a wave transmitted vover vthe path TAonly when those waves have at the point, in TA Where the con-` trolcircuit 9 is connected .thereto 'an' amplitude level sufficiently hightocause operation of the device 10 in control: circuit 9. An.- other-wayof accomplishing this would be to insert normally open contacts intheinput of control device 17 and to utilize an additional relay controlledb the operation of control device 10 to close t ese contacts when thedevice 10 is operated.

Control devices-10 andY 17 are both actuated by the telephoniecurrents,but with a time difference in operation of T seconds.

' The operation of relay 18 will therefore open normally closed switch24 in the input of con- `trol device 20 in control circuit 19substantially T seconds after the courier f2 is transmitted out over thecable TC. The switch 24.will remain open as long as speech currents arebeing vsubstantially continuously.

transmitted from the east terminal, and will revent courier f1transmitted ,over the cable TG from the West terminal station inresponse to the West to east telephonie currents, after'the courier f2is sent out from the east station, from reaching the input of thecontrol device 20 which controls relays 21 to 23. The relays 21 to 23cannot be operated, therevfore, by courier f1 or the following speechwaves, respectively, to disable `the .transymitting path TA by o'peningswitches 25 and 26-therein and to make operative the receivv ing path RAby closing switch 27. In the manner described the westwardly directed.

telephone currents at the east terminal have obtained complete .controlof the transmit- .ting and receiving circuits at the east teratthe eastterminal, but followed by a prime mark.

The courier f2, which 'is transmitted over the cable TC in advance ofthewestwardly directed speech waves by T seconds, on arrival at the westterminal station is impressed 0n the receiving circuit RA thereat byhybrid 'coil Hi. `The received courier f2 will be passed by the band assfilter 6 and then,

because the band passy lt-er 7 in the in'ain rel in, thus causing thewinding'oi relays 21 to 23. to be energized. .y

,Relay-23 willoperate to close the. normal ly open switch/"27' inreceiving path RA7 andthus make' that path operative for trans-`n1ission of the east to west speech waves from cable TC to thecircuitTL .15; Relays 21 and 22.' will simultaneously operate to interrupt 13 iiis .ceiving path RA will not v'ass the frequency. 120 f2, it willbediverted into t e control path 19" and initially operate controldevice 2Q there- 35 of relay 52.

45 operation.

' 10 of filter 35 therein is a third control circuit 49 comprising thcurrent-controlled relay controlling-device 0, and the relays 51 to 53connected in parallel to the output of con'- trol device 50.

Connected between the input of dela circuit 31 and the output of thetransmitting amplier 33 in transmitting circuit TA is a byvpass circuit54 com rising the yfilter 55 and the one-Way ampli er 56.

4 A'normally closed switch 57 located in the receiving circuit 'RAbetween the output of bandpass filter 34 and the point of connection ofcontrol circuit 49 to receiving circuit RA is adapted to be opened bythe operation of relay 48. A normally closed switch 58 located intransmitting circuit TA .between the hybridv coil l-I2 andthe point ofconnection of control circuit 37 to transmitting circuit TA is adaptedto be opened by 'operation of relay 51. Another normally closed switchv59 connected in transmitting circuit TA between the hybrid coil H1 andthe outputs `of'transmitting amplifiers 33 and 56' is adapted to beopened by operation A normally closed switch 60 located in controlpath'46 in the input of control device 47 therein is adapted to beopenedv by operation of relay 53.

The terminal-,circuit which has just been 40'. described is also of thesemi-biased type, but

in this case the circuit is normally operative for` transmission in4thevdirection from west to east, and vtransmission in the directionfrom east to westvdepends upon a switching The control lthe circuit ofFig. 1,.

The delay circuits 30 and The delay circuit 30 is designed to provide adelay of t seconds in .the transmission of the alternating rcurrentsytransmitted therel through where tis very small in comparison 55 to thetotalltransmission time T of the cable TC between the eastand westterminal sta'- tions. The delaycircuit'31 is designed to introduce adelay of T seconds in the transmission of alternating currents passedthere- '69 through.

The filters 32, 34, and 55 are'similar to the filters in the circuit ofFig. 1. The fil- .ters 32 and 35 are designed to pass frequencies withinthe speech frequency range and *J to suppress courier frequencies flandf2.'

devices 38, 47 and 50 are Asim-i ilar to the" control devices 10, 17land 20 in l 31 are similar to, 50, the Idelay circuit 4 in the circuitof Fig. 1.

The filter 55 is designed to pass the courier frequency f2 generated bythe generator 43' and to suppress other` frequencies. I ilter 34is'designed to pass the courier frequency f1 generated at the westterminal'station and frequencies within' the speech frequency range,yandpto suppress the courier frequency f2. Amplifiers 33, 36 and 56 andthe relays 39 to 41, 48 and 51 to` 53may be of any of the types wellknown in the prior art.

It" will be assumed that telephonie currents for transmission from eastto west are set up first at the east terminal station, and not more thanT seconds .later where T is the total transmission time of the cable,telephonic currents are set up at the West terminal, station fortransmission from west to east.

The westwardly directed telephonie cur- .rents'from the source TL areimpressed upon the input of transmitting circuit TA through hybrid coilH2. A portion of these impressed currents will be diverted into controlcircuit 37 and operate control device 38 therein causing the windings ofrelays .39, and 41 vto be energized. Relay`39 will operate to closenormally open switch in the transmitting circuit TA so as to make thatcircuit operative for transmission of the speech .waves between sourceTL and the cable TC.

Fast-operating relay 40'operates to close switch 42, thus connecting thegenera/tor 43 of frer ency f2 across the transmission circuit T Aninstant later slow-operating rclay 41 operates to open normally closedswitch 44, thus disconnecting the generator 43 from transmitting circuitTA. The momentary connection of generator 43 to transmitting circuit TAwill cause a short impulse of current of frequency f2, which will bedesignated hereafter as courier f2, to be rtlxw'iansmitted over thetransmitting circuitv A portion of this courier f2 will be diverted intoby-pass circuit 54, passed by the filter therein, amplified by amplifier56,im pressed by hybrid coil Hl'on cable TC and directly transmittedthereover to the West terminal station, where it will be effective toestablish initial control of the circuit thereat in a manner which willbe described later.

The portion of the courier f2 not bypassed th rough circuit 54 will passthrough delay circuit 31 being delayed therein for the time T. and, asfilter- 32 is designed not to pass the frequency f2, will vbe divertedinto control path 46 to operate control device 47, causing the windingof relay 48 to be energized. The lrelay 48 will then, operate to openthe normally closed switch 57 in receiving circuit RA; Due to the delayproduced inthe diverted courier by delay circuit 31, the switch 57 willbe open to disable path RA substantially 'l seconds after the courier f:has been lfill CII mageos cuits at the stationby unbalanced receivedenorgy orby energy stored in the delay circuit 4 prior` to the operationof control device 20. The westwardly directed speech wave which followsthe courier wave in transmis-- sion over the cable TC by the timeinterval T seconds, on its arrival at the west terminal station willalso be impressed by the hybrid coil H1 on the receiving circuit RA andpassed by the band pass filter 6', which, as stated above, is designedto pass the speech frequency bandas well as the frequency f2. A portionof the speech wave passed by the filter G', will be diverted in theoutput thereof into control circuit 19 and will be impressed on theinput of control device 20 so as to maintain that device in the operatedcondition initiated by the preceding courier f2. The relays 21 to 23will therefore be maintained operated as long as speech is beingreceived over the cable TC from the east terminal station. and thus willmaintain the receiving circuit RAloperative and the transmitting circuitTA disabled for that length of time.

The main portion of the speech currentsin the output of the band passfilter 6 in receiving circuit RA will be supplied to the band passfilter 7 therein, passed by that filter, amplified bythe receivingamplifier 8 and transmitted from the output thereof to the circuitI TL.

lt is readily seen that because of thev particular relation oi' thedelay produced in transmitted waves by delay circuits i and a at theeast and west terminals, respectively, to the transmission time of thecable TC, that whichever terminal first 'sends out its courier impulsewill gain exclusive control of both sets ot terminal apparatus. Becausethe speech energy from cach station is not impressed upon the cable TCuntil after the initial operation ot the switching apparatus at the tarterminal by the irst courier to be transmitted, the incoming courierneed not be selected in 'the presence of simultaneously outgoing speechenergy and there will be no loss of speech because ot interferencetherewith.'

" of control devices l() and 17 will need to be very accuratelymaintained ifkthe different rates of speech energyin the case of dierent-ivords are not to introduce deviations in the relative operating timesof the two control devices. i

Fig. 2 shows a modification of the circuits of the terminal station of Fig. 1 in which the device controlling the disabling of the receivingcircuits in responseto energy to be transmitted, corresponding to thecontrol device 17 of F ig. 1, is operated under all conditions verypositively and in a deinite time relation with respect to the time inXwhich the courier is sent out over the cable. This is accomplished bycausing this control device to be initially operated by a local courierimpulse suitably -delayed with respect to the courier impulse sent outover the cable instead o'f by the delayed speech impulseonly.

In the terminal station of Fig. 2 (which is the east station), theoutput of the transmiting circuit TA and the input of the receivingcircuit RA are associated in energy transmitting relation with the cableTC and in conjugate relation with each other, as the system of Fig. 2,by a hybrid coil H1 and its associated balancing network N1, and theinput of the transmitting circuit TA and the output of the receivingcircuit RA are coupled in conjugate relation with each other, and inenergy transmitting relation with the circuit TL through the hybrid coilH2 and its associated balancing network N2. The transmitting circuit TAcomprises, connected between the hybrid coil H2 and hybrid coil H1reading from eastl to west, the one-way delay circuit 30,the one-waydelay circuit 31, band pass filter 32 and the transmitting amplier- 38.The receiving circuit RA comprises, connected between the hybrid coil H1and the hybrid coil H2 reading 'from west'to east, the band pass lter,the band pass ilter 35 and the receiving ainplier 36.

Connected to the transmitting circuit TA between the hybrid coil H2 andthe input o delay circuit 30 is a control circuit 37 comprising thecurrent-controlled relay controlling device 38, and the relay 39,quick-operating relay a0 and slow-operating relay al connected inparallel to the output of device 38. The normally open switch i2connected to a say ico

source e3 of alternating current of a ref quency ,'fz, which frequencyis outside the speech frequency range, is adaptedto. be closed byoperation cit the relay 40 to conneet the source 113 acrossthetransmitting circuit TA at a point between the output of delaycircuit 30 therein and the input of delay circuit 31 therein. A normallyclosed switch 44 connected to the circuit TA, and source i2-l is adaptedto be opened by operation of relay t1 to disconnect the source 43 fromthe transmitting circuit TA. A normally open switch` l5 located in thetransmitting circuit TA between the output of delay circuit 3() and thepoint of connection ot the source 43 to the transmitting circuit TA is,adapted to be closed by operation of relay 39.

igeaaeae f transmitted out'over the cable TC, and therefore will preventcurrents which arel sent out over the cable TC from the west terminalstation after courier f2 has been transmitted thereover from the eastterminal station from reaching the input of control device in controlpath 49 and causing its operation, and therefore the operation of relays51 to 53 to disable the transmitting path TA.

The main portion of the westwardly directed speech currents are delayedin transmission over the transmitting circuit TA for zf-fT seconds 'dueto the action of delay circuits 30 andr'Sl therein. I The small delay oft seconds produced by delay circuit 30 insures that the switch 45 hasbeen closed to make operative the transmitting path TA and that controldevice 47 in control path 46 has been operated by the preceding courierbefore the speech currents arrive thereat.

The portion of the delayed speech currents in the output of delaycircuit 31 which is diverted into control circuit 46 and impressed onthe input of control device 47 serves to maintain that device in theoperated condition initiated by the preceding courier f2. Relay 48controlled by controldevice 47 will therefore be maintained operated aslong as speech currents are being transmitted into control circuit 46. I

The main portion of the speech currents in the output of delay circuit31 will be passed by the band pass lilter 32 in transmitting cirlcuitTA, amplified by the transmitting amplifier 33 therein, impressed bymeans of hybrid coil H1 upon the cable TC and transmitted thereover tothe West terminal station T-l-t seconds behind the precedingcourier f2.

Thev manner in which complete control of the transmitting andy receivingcircuits at'the west terminal station is obtained for the east terminalstation will be vclear from the following description by reference tothe receiving circuits at the east terminal station. The apparatus atthe west terminal station corresponding to that at the east terminalstation will be designated with the same characters as the latter butfollowed by a prime mark.

The portion of the courier' f2 transmitted over cable TC from the eastterminal station, on arrival at the west terminal station will heimpressed by hybrid coil H1 on the receiving path RA and passed by theband pass .is filter 34 therein, which filter is designed to passfrequencies within the speech-frequency range and the courier frequencyf2 and to suppress the courier frequency f1 (which is the courierfrequency generated atthe west stal tion). As filter 35 is designed notto pass the frequency-f2, the courier f2 inthe output of.

the band pass filter 34 is diverted into control circuit 49 andinitially operates control device 50 causing the windings of relays 5l,ci to 53' in the output thereof to be energized.

Relays 51 and 52 immediately operate to open normally closed switches 58and 59',

respectively located in the input and output of the transmitting circuitTA making that circuit inoperative to transmit speech currents 0r thecourier f1 generated by generator 43 to the cable TC. Relay 53simultaneously operates to open the normally closed switch 60 in controlcircuit 46. The disabling of the transmitting circuit TA in the severalplaces is for the purpose of preventing false operation of controldevice 47 by unbalanced received energy or energy which may be stored indelay circuits 30 and 31 prior to the operation of control device 50.

The speech wave from the east terminal station following the courier f2over thecable TC by the interval of time T-i-t seconds on arrival at thewest terminal station will also be impressed u on the receiving pathiRAby the hybrid coll H1 and passed by the band pass filter 34 in the inputthereof. These speech Waves in the outputy of the band. pass filter 34will be divided between the control circuit 49 and the main receivingpath RA. rilheportion diverted into control circuit 49' control device50 and serve to maintain that device in the operated condition initiatedby the preceding courier frequency f2. The relays 51 to 53 1n the outputof control device 50' will therefore be maintained in the operatedcondition `as long as speech waves from the east terminal station arebeing received by the receiving circuit RA from the cable TC.

IThe main portion of the westwardly directed speech waves in the outputof the band pass filter 3 4 will be transmitted over the main receivingpath RA', passed b the band pass filter 35 therein, amplified y thereceiving amplifier 36 and impressed by the hybrid coil H2 upon thecircuit TL.

In the manner which has been described,

complete control of the transmitting and re-v ceiving circuits 'at botheast and west terminal stations has been obtained yfor the east terminalstation. If the speech Waves to be 4transmitted had been first set up atthe west terminal station, the latter station would have obtainedcontrol of the transmitting and rewill be impressed upon the inputcircuit of ceiving circuits at both terminals in a similar manner. v

Fig. 3 shows the circuits of an intermediate repeater station'which maybe used for connecting two sections of the cable'TC, an east section TC2leading to an east terminal stan tion auch as illustrated in Figl or2and a west section TC1 leading to a similar west terminal station. Thecircuits of this intermediate repeater station are'arranged so that theterminal station which first sends out its courier gets complete controlof the lintermediate repeater circuits as well as those of the twoterminal circuits.

. The circuits ofthe intermediate repeater station comprise a.westwardly directed amplifying-path WA and aneastwardly directedamplifying path EAhaving a portionCA in common. The inputof the path WAand `the output ofthe vpath EA are coupled in 4energy transmittingrelation-with the west end of the east cable section TC2 and in con---jugate relation to each other by means of H3 and associat d .balancingnetwork N3.

. Similarly, the input ofthe ypath EA and the output of the path WA arecoupled in con- 1.fjugate relation to each other and in energy ..5

transmitting relation with the east end of the west cable section TG1 bythefhybrid coil H4 and its associated balancing network N4. The'.westwardl directed amplifying path WA comprises etween the hybrid coilsH3,`

and H.L in order from east to west, the bandv pass filter. 60, theone-'way amplifier 61 and the transmitting amplifier 62, while the east-.wardly transmitting path EA comprises connected-b'etween the hybridcoils H4 and Hg in order from west to east the band pass filter 63, theone-Way amplifier 64 and the transemally'closed switch 71controlledbyfthe re- 72 is located in the amplifying path EA the outputof filter'63 andthe input between f of amplifier 64. l.

' The one-'way-amplifier 64 in the path EA vand the one-way amplifier 61in the path WA are for the purpose of preventing transfer of speechcurrents between these paths at their junction with the common branchCA.. This may be prevented'byl the use of other means, `fo'r example, abalanced bridge at the junction of paths EA, WA and CA, suchasdisclosedin Fig. 8 ofl my United States PatentrNo. 1,695,813, issuedDecember 18, 1928.

A westwardly directed one-way by-pass circuit BW is connected betweenthe output vof filter in amplifying path WA and point-s in the output ofpath -WA between the switch65 therein and the hybrid coil H4.

' Similarly, an eastwardly directed4 one-way by-pass circuit BE- is'connected between the 'output of filter 63 in the amplifying path EA land points in the voutput of said path lie-- tween the switch 67 thereinand the hybrid Q coil H35 The by-pass circuit BW comprises in order fromeast to west the band pass filter 65' 73, the band pass fiter 74, theone-way amthe three-winding transformer or hybrid coil W between thefilters 7 Sand.

4 therein is a control circuit 79 comprising the delay circuit/80, thecurrent controlled relay controlling device 81, and the relays 66,

72 and 83 connected in parallel to the output of the control device 81.Similarly connected to the by-pass circuit BE between filters 76 and 77therein is the control circuit 84 comprising 'a delay circuit 85, thecurrent controlled relay controllingdevice 86, and the V relays 68, and87 connected in parallel to the output of control device 86. A normallyclosedu switch 88,J4 which vis controlledby the relay 87 is located' inthe control circuit 79 between the'output of the delay circuit 80 andthe input of control device 81therein. Similarly,.a normally closedswitch 89 is located in the control circuit 84 between the output ofdelay circuit 8 5. and the input of the control device 86 therein. j

The control devices 81 and 86 are similar to the control devices' usedat 4the terminal stations shown in Figs. 1 and 2.

The delay circuits and 85 located in coni trol paths 79 and 84,respectively, vare similar to the delay circuits .used at the termin-alstations shown in Figs. 1 and 2. Delay circuit 80 is designed, toproduce a delay in the currents transmitted ltherethrough ofsubstantially T1 seconds where'Ti is the total transmission time of thewest cable section TG1 between tl'iefintermediat'e repeater station andthe West terminal station. Similarly, delay circuit 85 is designed tointroduce a delay in the currents transmitted therethrough ofsubstantially T2 seconds, where 'll2 is the total transmission time ofthe east cable section TG2. Y l

For proper operation of the system it is only necessary that the totaltime of transmission from the east terminal station to the controldevice 81 at the intermediate repeater is substantially equal to thetotal time of' transmission from the west terminal station to thecontrol device 86 at the intermediate repeater. lf the transmission timeT1 of cable TG1 is greater than the transmission time T2 of cable T02,the delay time of delay cir-` cuit 85 may be 0 seconds, that is,delayfcircuit 85 may be eliminated, and the 'delay time of delay circuit80 made 'T1-T2 seconds or -if T2 is great/er than T1 the delay time ofdelay circuit 85 may be made 'T2-*T1 seconds and the delay time of delaycircuit 81 made zero, that is, the latter may be eliminated. Filter 60in the amplifying path WA, filter 63 in the amplifying path EA, filters73 and 74 in the by passcircuit BW and filters 76 vand 77 in the' bypasscircuit Blf/are similar tothe filters used at the terminal .stationsshown in Figs. 2- and .3. The ,lter 66 istieisa nsaaeoe signed to passfrequencies Within the speech lfrequencyfrange and the courier frequencyf2 generated at the east terminal station and to suppress courierfrequency f1 generated at the west terminal station. Similarly, filter63 is designed to pass frequencies Within thev speech frequency rangeand courier frequen-y cy f1 and to suppress courier` -frequency f2.Filter 73 is designed to' pass frequencies Within the speech frequencyrange and the courier frequency and to suppress Waves of otherfrequencies, while ilter 7 4 is designed to pass the courier frequencyf2 and to suppress lWaves of other frequencies. Filter 76 is designed topass frequencies Within the speech lfrequency range and thecourierfrequency f1 vthan T seconds later where T is the totaltransmission time over both sections of the cable TG1 and TG2 andtherefore equals Tl-l-'lz seconds, speech Waves for transmission fromeast toA West are set up at the east terminal station. llt will beassumed that the transmission time' T1' of the cable section TG1 is`greaterthan that of the cable section TCL..

' cable section TC, T seconds in advance of the speech vvavesin themanner which has been described in connection with the terminal circuitsof Figs. l and 2. The courier f1 on arrival at the intermediate repeaterstation will be impressed by hybridl coil H4 thereat upon theeastvvardly ldirected amplifying path EA and passed by the lter 63therein. ln the output of the filter 63 the courier f1 will divide. Theportion trans mitted over the path EA will be dissipated therein due tothe normally open switch 67 in the output thereof. The other portion ofcourier f1 will be passed by the band pass filter 7 6 in the byc-passcircuit BE and will divide in the output thereof. A portion will be Vba-nsmitted over the by-pass circuit BE being passed .by iilter 77 andamplified by amplifier 7 8 therein. rlhe amplihed courier f, will thenbe impressed on the east cable `section. TS2 by hybrid coil H8 andtran..n

mitted directly thereover to the east terminal station to initiallyoperate the control appa-- ratus thereat in the manner previously de?scribedin connection with AFigs. 1 and 2.

The other portion of the courier f1 in the output of filter 7 6 will bediverted into the control circuit 84 and will be transmitted throughdelay circuit 85, which according to our assumptions will introduce zerodelay, and then will initially operate control device 86, `which in turn`Will cause the windings of relays 68, 70 and 87 to'be energized. vRelay70 `will operate to open the normally closed switch 69 in the inputofamplifying path WA to disable that path for the transmission of currentsfrom the output of filter 60 to amplifiers 6l and 62. Relay 68 willoperate to close the normally open switch 67 in the output of theamplifying path EA, making that path operative'for the transmission ofcurrents in the west to east direction between cable sections TG1 andT02. Relay 87 will operate to open the normally closed switch '88 in thecontrol circuit 7 9, making that circuit inoperative for thetransmission of currents from the output of lter 73 in by-pass circuitBW to the input of control device 8l in control circuit 79.

Relays 68 and 76 should be relatively adi'usted so that switch 69 inamplifying circuit WA opens to disable that circuit before switch 67 inamplifying circuit EA closes to make circuit EA operative, thus avoidinga singing path. The relays 72 and 66 associated with control circuit 79should be similarly relatively adjusted for a similar purpose.

lhe eastivardly directed speech currents following the courier f1 intransmission over the cable section TCLby the time interval of T secondsupon arrival at the intermediate repeater station will also be impressedby hybrid coil Hi upon the eastwardly directed amplifying circuit EA andpassed by the filter 63 in the input'thereof. A portion of the speechcurrents in the output of filter 63 will be transmitted over theby-pas's circuit BE and passed by the filter 76 therein. As the lter`77is designed. so as not to pass waves vvithin the speech frequency range,this p0rtion of the speech currents will be diverted into controlcircuit 8a and after passing through delay circuit 85 having a delay ofzero seconds Will be impressed on the input `of control device 86 tomaintain that device in the operated condition initiated by thepreceding courier as long as the speech Waves are being continuouslytransmitted from cable section TG1 to cable section TG2 in theeastwardly direction.

The main portion of the speech waves in the output circuit of filter 63will be transmitted over the eastwardly directed path EA, amplified inamplifiers 64 and 62 therein, and, as the normally open switch 67 inpath EA is now in the closed condition due to the action of thepreceding. courier frequency. f1,

' .and the control path 79 inthe manner which has just been pointed outwill prevent the courier f2 from the east terminal station, whichaccordingto our assumption,I would not be'started over cable section'TG2 until after the'courier 1 from the west terminal station has starteout over the cable section TG1-.to the intermediate.- repeater station,

' pressed by from setting up a singing circuit, or being effective tooperate control device 81 and thus to seize control of the intermediaterepeater apparatus for the east terminal station..

The operation of the intermediate repeater station for the case when thespeech waves for transmissionv from east to west are set up at the eastterminal station before the speech Waves for transmission from west toeast are set up at the West terminal station is similar to the o rationWhichhas just been described. In this case the courier f2 received overcable section TG2 Will be passed by lter in the inputof the amplifyingpath WA and lilter .7 3 in by-pass circuit BW. A portion thereof will bepassed by filter 74, lampliied by amplifier 7,5, impressed on the westcable section' TG1 and transmitted thereover to initially operate thecontrol of the switching apparatus at the West'terminal station in themanner which was described in .connection with Fi s. l andQ. The otherportion of the courier g 2 inthe youtput of filter 73 in bypass circuitBW will be diverted into the con trol circuit 79 andafter being delayedtherein for-Tf-TB seconds according to our assumptions, by the delaycircuit 80 will operate control device 81 toinitially operate the relays72, 83 and 66 so as to first open'the normally closed switches 71 and 89in amplifying pat 1 EA and the-control circuit 8d, respectively, andthen to close the normali open switch inampliying path EA. T e speechWaves transmitted from the West terminal station T seconds behind thecourier f2" on arrival atl the intermediate repeaterstation will beimthe hybrid lcoil H3 upon the amplifying path WA and passed by thefilter 60 1n the input thereof. A small portion .of the speech vWaves inthe output of the filter 60 Will be passed by the filter 73 in theby-pass circuit BW and will be diverted into the control path 79 andlafter being delayed for -T1--T2 rseconds in the delay circuit 80 willbe impressed on the input of control device 81 so as to maintain thatdevice 1n the operated condition initiated by the preceding courier aslong as speech waves are being continu-V ouslyl received for the cablefsection TG2. The repeater circuits having been conditioned in the mannerdescribed, the main portion of the speech currents in the output ofilter 60 will be transmitted over the amplify ing path WA amplified vbyamplifiers 61 and 62- therein and impressed. on cable section TG1 andtransmitted thereover to the west terminal stati0n,"where a smallportion thereof will be utilized to maintain the switching circuitsthereat in the condition initiated by the receding courier and the mainportion will e delivered to the receiving circuits in the mannerdescribed in ldetail in connection with Figs. 1 and 2..

The disabling of the' amplifying path EA and the control path Sellin themanner which has just been described Will prevent the .courier' f1 andthe succeeding speech Waves from the west terminal station from beingedective to seize control of the intermediate repeater apparatus.

The relation of the delays produced by the delay circuits 8,0 and 85 inthe control circuits I 79 and 84, respectively, at the intermediaterepeater station, to the transmission times of the two cable sectionsvTG1 and TG2 insures that complete control of the intermediate repeateris given to that terminal'which first starts its courier on its way.

'It is to be understood that the invention is not limited to theparticular circuits, and details ofthe particular terminal andintermediate repeater stations `illustrated and described as numerousmodifications thereof may be made by persons skilled in the'art withoutdeparting from the spirit and scope of thel invention. For example,although the terminal stations which have been illustrated and describedcomprise either a normally operative' receiving circuit, a normallydisabled transmitting circuit and switching means responsive to Waves tobe transmitted to disable the receiving circuit and make operative thetransmitting circuit, or a normally operative transmitting circuit, anormally disabled receiving circuit and switching means responsive toreceived waves to render the receiv.' ing circuit operative and todisable the transmitting circuit, itis apparent that the invention maybe applied to other types of terminal circuits; for example, to terminalstations comprising normally disabled receiving and transmittingcircuits and switching means responsive to transmission ineither-direction to make the circuits operative tor that direction.

Although the intermediate repeater station which has been illustratedand described comprises normally inoperative amplifying paths for thetwo directions of transmission "having aportion in common, and switchingcircuits responslve to transmission 1n either- Lacasse direction to makethe amplifying path in that direction operative, it is apparent that thein- -vention is not limited to thatJ type oi' interf mission have noportion in common, or in which one path is normally operative and theother path normally disabled and the switchin circuits are responsive totransmission in eit er direction to make the amplifying pa-.hs operativeto repeat the transmission in that direction only. l l,

Although in the terminal circuits which have been illustrated and'described, the receiving circuit or the transmitting circuit in somecases has-been shown normally disabled,

or adapted to bedisabled, in a single place, because of the high gain.which may be used in terminal rircuits of this t e it may be desirableto have the 'transmitting and receiving circuits normally disabled or`adapted to l be disabled in several places.

Although 'n the particular embodiments of the invention which'have beenillustrated and described mechanical relays have been employed forconditioning the transmission paths by operating movable switches toclose or open circuit these paths, the invention is not limited to theparticular means shown. For example within the scope of the inventionthe transmission paths may be effectively disabled by short circuits orloss networks inserted in the paths, controlled by current'controlledrelays. Stationary devices having no movable elements may be employed inplace of the mechanical re ays, for example, vacuum tnbefrelays, such asdisclosed in Crisson lUnited States Patent l1,647.212. issued Novemberl, 1927 or in the article by C.. A. Beer andG. T. Evans, in theinstitute of P. 0. Electrical Engineers '(London), vol. 20, parres to 72inclusive, published in 1920. v

What is claimed is:

1. ln a signal transmission system comprising a signal transmission pathover which the time of transmission is appreciable and in which two-Waytransmission is secured by signal-controlled circuit-control means. themethod ot avoiding mutual lockouts of transmission and consequent lossof part ot' the signal transmission. which consists in establishingcontrol of the circuitlcontrol means by means of a short train ofcontrol Waves sent over the system. and delaying the application ofsignals to the transmission path until such control is established.l

2. The method of operatingv a signal-directed two-Way transmissionsystemincluding a signal transmission medium over which the time oftransmission is appreciable, vvhich consists in transmitting a. shorttrain of control waves over said medium under control of the signals tobe transmitted, to condition the system for the transmission of saidsignals thereover, and delaying the application of the signals to thetransmission medium by a time approximately equal to the overalltransmission time of said transmission medium.

' 3. transmission system com rising a signal transmission path supplied'rom a source of signal Waves, control means `for determining theoperation of said path, means under the control of said signal Waves for.transmitting to said control means and in advance of the signals animpulse of current'to initially operate said control means, means todelay the sending out of the signal Waves over said path at least untilsaid control means has been initially operated by said impulse ofcurrent, and means for utilizing the delayed vsigii'lwave when itarrives at the control point to maintain said control means in itsinitially operated condition.

4. A s stem for the two-Way transmission ot signa ing currents includingcurrent-controlled means at av oint therein for conditioning the systemor efficient operation in the direction of transmission, means'atanother point in said system and controlled by the signaling currentswhen they arrive thereat for causing a momentary .impulse of.

control current to be transmitted over the system in the direction ofthe controlling signalingcurrents to initially actuate saidIcurrent-controlled means, means for delaying the transmissionpof thesignaling currents over said system .from said other point for aninterval of time at least equal to the Wave transmission time of saidsystem from said other point to the control point.I and means forutilizing the delayed signaling currents when they arrive at the controlpoint to maintain said current-controlled means in its initiallyoperated condition.

5. A system for the two-Way transmission.

of telephonie currents comprising a two-Way line, stations lat variouspoints along said line and comprising oppositely directed amplifyingpaths for said currents, currentcontrolled means at said stationsresponsive to transmission of waves'in one direction for conditioningthe amplifying paths thereat for efiicient transmission in said onedirection only, and responsive to transmission of waves 1n the oppositedirection for conditioning said paths for efficient transmimion in saidopposite direction only, means at one of said stations and controlled bthe transmission of telephonie currents in t e amplifying path thereatfor said one direction, for causing a momentary impulse of controlcurrent to be transmitted over the system in the direction of thelcontrolling vtelephonie currents to .initially operateI thecurrent-controlled means at another of said stations, means to delay thetransmission of saidtelephonic currents from said one station to saidline for an interval of time at least equal to the transo' positelydirected amplifying paths for sald lcurrents, means at each stationresponsive `mission time over said system from said one station'to saidother station, and means for utilizin the delayed telephonie ,currentswhen tiey arrive lat said other station to maintain thecurrent-controlled means thereat in the Condition initially produced bythe preceding impulse of current. 6. A system for th two-waytransmission of' telephonie-currents comprising a two-way lineconnecting stations each comprising opto transmission over the system inone direction for conditioning said paths for eiiicient operation insaid onel direction only, and relsponsive to transmission over thesystem in the other direction for conditioning said paths for eiicientoperation in vsaid other direction only, and means for insuring completecontrol ofthe-'conditioning means at both stations to the one of saidstations at which telephonie current transmission )firstv starts, thelast mentioned means comprising at each station' means controlled by thetelephonic currents to be transmitted therefrom for sending out oversaid line an impulse of current to initially operate the conditioningmeans atthe other station, means for delaying the transmission of thetelephonie currents to said line for an interval of time after.

said impulse has been sent out thereover which is substantially equal tothe transmission time of said two-way line between said stations,meansfor utilizing the delayed telephonic currents as they arrive at saidother station for maintaining the conditioning means thereat in theirinitially operated con dition, and means for preventing incomingcurrents from the other station, if started v'therefrom over said linelater than the impulsey from the first station, from being et- ,tectiveto operatethe conditioning means at said first station untiltransmission of the telephonie currents `initiating the impulse, fromsaid first station is interrupted for a time interval at least equal tothe usual pause between sentences.

7. The system of claim 6, and in whichV the last mentioned means iscontrolled by the delayed telephonic currents at said first station.

S. ln a system for thetWo-way transmission of signaling waves, a two-wayline having an overall transmission time of T seconds of current hasbeen transmitted thereto, means responsive to currents recelved by saidreceiving circuit from said line for effectively disabling saidtransmitting circuit and making operative said receiving circuit, andmeans responsive to the delayed signaling Waves for disabling the lastmentioned means for operation by said received currents untilsubstantially continuous transmission of signaling Wavesfrom said sourceto saidl transmittingcirc'uit has been interrupted for an appreciableinterval of time.

9. ln a system for the two-way transmission of signaling wavescomprising a two- Way line having an overall transmisslon tlme of T,seconds and a station comprising a `for impressing a portion of saidimpulse ofv control'current upon sald llne for transmlssion thereover,means for delaying transmission of said signaling Waves to said lme fortransmission thereoverfor substantially T+t 'mounds after-said portionof control current has been transmitted thereto, Where t is very smallin comparison to T, means re1 sponsive to currents received from saidline by said receiving circ-uit for efi'ectively .disabling saidtransmitting circuit for the transmission of waves from said source tosaid line, means for utilizing the other portion ofk said controlimpulse for disabling said receiving circuit and said transmittingcircuit, for o eration by said received currents, substantially Fllseconds after the first portion of said control impulse has beentransmitted to said line and means responsive to the delayed 'signalingWaves for maintaining said receiving circuit and said transmittingcircuit, disabling means disabled until transmission of signaling wavesover said transmitting circuitY has been interrupted for an appreciableinterval of time.

10. ln a system for the two-way transmission of signals, a repeaterconnecting a West section of a 'two-Way line having an overalltransmission line of T1 secondsand an east section of 'a two-way linehaving an overall transmission time of T2 seconds, said repeatercomprising an eastwardly directed one-Way amplifying path and a'westwardly directed one-way amplifying path `for'said signals'` bothpaths being normally disabled in their outputs, an eastvvardlydirectedone-way circuit for lay-passing a small portion of the signalsand Waves off certain characteristic frequencies outside thefrequency'range of said signals received over said West Section of linearound said repeater to said east section of line, a Westwardly directedone-Wa circuit for ley-passing a portion of the signals and other Wavesof characteristic frequencies different from said certain frequenciesand c outside the frequency range of said signals,

lill

around said repeater to said West section of line,` a control pathconnected to the east- Wardly directed by-pass circuit for diverting aportion of the Waves transmitted thereover and including means fordelaying the diverted Waves therein`T2 seconds, another control pathconnected to the westwardly directed b -pass circuit, for divertin aportion of t. e Waves transmitted thereover and including means fordelaying the diverted Waves therein for T1 seconds, means responsivetothe delayed, diverted Waves in the first mentioned control path fordisabling said westwardly directed amplifying path in its input, andsaid other control path, and for making said eastwardly directedamplifying path operative, and means responsive to the delayed, divertedWaves in said other control path for disabling said eastwardly directedamplifying path in its input, and the lirst mentioned control path andfor making operative the Westwardly directed amp fying ath. f p ll. In asignaling system in which exclusive control of a stationfor'transmitting or for receiving is seized through the agency .f of thelsignaling Waves entering the system,

the method comprising directively'seizing control of a transmitting anda receiving station iii-'response to signal Waves, and delayingtransmission, between the seized. stations, of the signals until sachcontrol has been established. y

12. ln a two-Way system for transmitting andreceiving signals over atransmission path of appreciableoverall transmission time, atransmitting and a receiving branch ata station, one of which isnormally operative and the other normally inoperative, signal controlledmeans to maire operative the normally .inoperative branch and to maireinop.

erative the normali operative branch to conv dition the station ortransmitting over said or receiving from. said path, means at .4

said station controlled by signals to be transmitted over said path foroperating said signal controlled means to condition the station so thatit can transmit signals to but cannot receive signals from path, meansfor deiaying` transmission of said signals to said forsubstantialiytheoveral transmission time of the path, and means for delayingconditioning the station so that it cannot receive for a timesubstantially egaal, the overall transmission time of said path afterconditionin of the circuit so it can tr. W,mit parte.a

y rebeive from said path by signals at said station to be transmittedover said path.

14. A system according to claim 12 in which said station is maintainedin condition to receive from said ath but is disabled to transmit tosaid path' y signals received over said path.

15. In a two-Way system for transmitting and receiving signals over a.Wave transmission path of appreciable overall transmission time, astation having connected to said path a transmitting circuit and areceiving circuit one of which is normally operative and the othernormally disabled, signal-controlled means to make operative thenormally disabled circuit and to disable the normally op- Y erativecircuit to condition the station for receiving from said path ortransmitting to said path, means at said station controlled by Wavesreceived over said path for operating said signal-controlled means tocondition the station lso that it can receive waves from said path butcannot transmit waves thereto, and means for delaying transmission ofsignals tol said path for substantially the overall transmission time ofsaid path.

16. A system according to claim 15 and in which said station ismaintained in condition to receive waves from said path and disabled fortransmitting signals to said path by the si als received thereover.

n Witness whereof, l hereunto subscribe my name this 10th da of J une1929a nos er c. harnas.

station is maintained in condition

